Mordant dye image and process of producing the same



Patented May 31, 1938 UNITED STATES PATENT OFFICE MOBDANT DYE MAGE AND PROCESS OF PBODUC'IIN G THE SAME I Rudolf yon Arx, Berlln-Wilmersdorr, Germany 5 Claims. (Cl. 95-88) My invention relates to theproduction of colored images, more particularly to the production of mordant dye images.

Several processes are.known by which photographic silver images can be transformed, by the medium of mordant images, intodyestufi images. These are what are termed mordant-dye processes.

By way of example, the Christensen'process, in which the active mordant is represented by cuprous thiocyanate, may be mentioned here.

Now it is the object of this invention to make known a process which, from its many-sidedness, is most specially suited for actual practice. The process is characterized by a maximum of insensibility (freedom from stains) and reliability. The disadvantage inherent to manyother mar;- dant-dye processes due to the fact that silver images of a character frequently of very particularly diflicult access are required as a base, is done away with here.

The active mordant compound in question here is theferrocyanide of zinc.

The converting bath may easily be prepared in such a manner that the converting reaction practically stops, leaving an image consisting of unattacked silver, ferrocyanide of silver and ferrocyanide of zinc. By this means, after the dyeing, mordant-dye images are obtained showing color tones of a pleasing effect due to residual silver.

Pure color tones, such as they are required, say, for purposes of color photography, can -.be obtained either by using a converting bath leaving no unattacked silver, or, again, by removing the silver residues, either before or after the dyeing process, by some agent capable of dissolving silver (for instance: diluted chromic acid). I

The ferrocyanideof silver, too, formed simultaneously with the ferrocyanide of zinc, can be easily removed, for instance with the aid of thio-.

After a short wash, the dyeing is done in a solution of malachite greenhaving thiscompositionz- 1 gm. of malachite green, 2 gms. of glacial acetic acid, 3000 cm; of water. The resulting mordant-dye image is. given a brief wash in water for the purpose of .removing from it any unmordanted coloring matter and may be allowed to remain in this condition, or, again, be desilvered by means of diluted chromic acid.

The desilvering can, if desired, be done prior to the dyeing process.

The ferrocyanide of silver is readily dissolved away with thiosulphate.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. The process of producing a mordant color image which comprises treating a photographic silver image with an aqueous solution contain ing a soluble zinc salt, a soluble ferricyanide, and a neutral salt of a strong base and a weak organic acid the anion of which is capable of forming with the zinc ion in the presence of hydroxyl ions 9. complex zinc-organic acid anion, thereby preventing the precipitation of zinc ferricyanide, the dilution of said aqueous solution being adapted to bring the reaction to a standstill in a short time with the conversion of no more than a part of the sliver of the silver image into zinc ferrocyanide and silver ferrocyanide, and then converting the image into a mordant dye image by treating it with an aqueous dyestufl solution.

2. The process of producing a mordant color image which comprises treating a photographic silver image with an aqueous solution containing zinc sulphate, potassium ferricyanide and potassium citrate, the dilution of the solution being adapted to bring the conversion of no more than a part of the silver of the silver image into zinc ferrocyanide and silver ferrocyanide, and then converting the mordant image into a mordant dye image by treating it with an aqueous dyestufl solution. 3. The process of producing a mordant color image which consists in treating a photographic silver image for a few minutes in a bath containing 1.6 gms. of zinc sulphate, 16 gms. of neutral potassium citrate and 1.6 gms. of potassium ierricyanide per litre of water, and then converting the image into a mordant dye image by treating it with an aqueous dyestuff solution.

4. In the process claimed in claim-'1 the step of dissolving unattacked silver out of the mordant image prior to converting the. latter to a Y mordant dye image.

5. In the process claimed in claim 1 the step of dissolving unattacked silver outof the mardant dye-image.

'BUDOLF von ARK. 

